Fuel pump shut off

[Damian]

Im troubleshooting a situation on my Ty where the fuel pump won't kick on when I go to start the truck up. If I connect 12 volts to the wire by the distributor, the pump does turn on. I've also swapped relays around with the same no kick on results. I've checked the voltages at the plug and sometimes I get the trigger wire voltage, sometimes I don't. I checked that with the 12 volts to that wire by the distributor. The only thing I can think of is the oil pressure sometimes shows pressure when cranking and sometimes it doesn't. If the truck is running, it does show oil pressure. If I try to run the fuel pump with the relay only, it shuts off as soon as I take power off that testing wire. I've already fried a borrowed ECU, and I'm not really wanting to fry another.

Things I've changed is the whole distributor, coil, new plugs, and added more grounds directly to the alternator casing. I thought I fixed it when I added the grounds, but the next day it refuses to start no matter what I do. I've checked all of my grounds and they are in good shape and hooked up. When it did run, it ran great, super smooth. One thing, when it was running once, I opened the door and the lights dimmed and the CEL flashed on for a second. Hence why I added and checked grounds. Fuses are all good too.

Is it even possible that my new oil pressure sensor works intermittently? I'm not good at troubleshooting electrical stuff to be completely honest. Any ideas??

 

[Sydwinder905]

Re: Fuel pump shut off

does the pump kick on for the first couple seconds after you turn the ignition to RUN?

 

[Damian]

Re: Fuel pump shut off

No.

 

[canadian]

Re: Fuel pump shut off

The pump should cycle for a second or two when you turn the key into the IGN position to build fuel pressure before starting the truck. Test for voltage at the fuel pump connector by the tank when you first put the key in the ACC position to see if you get 12v.

 

[Sydwinder905]

Re: Fuel pump shut off

you've got yourself a problem on the control side then. you said you hot wired the pump by supplying voltage at the relay so you've already tested circuit integrity from there all the way to the pump. so im thinking your problem lies in the relay itself not getting a signal voltage from the pcm. check for voltage at the relay for supply voltage. Note: checking this may be a bit of a PITA because once you turn the ignition on you will only have a couple of seconds to check it.

 

[Damian]

Re: Fuel pump shut off

I've checked it already. Sometimes it's there, sometimes it's not. It's very random.

 

[Sydwinder905]

Re: Fuel pump shut off

next step is to check wire continuity all the way to the pcm, if tests ok and is not shorting, test for voltage directly at the pcm.

 

[ppress79]

Re: Fuel pump shut off

oil pressure switch is bad.

Phil

 

[Damian]

Re: Fuel pump shut off

next step is to check wire continuity all the way to the pcm, if tests ok and is not shorting, test for voltage directly at the pcm.

Which wire at the ECU am I looking for? Seriously, my electrical skills are very limited. My volt meter is a cheapo from Harbor Frieght.

oil pressure switch is bad.

Phil

Would the oil pressure switch work here and there? It's a PITA to get to, and I have no problem changing it if I have to, just tired of spending tons of money on it with no changes.

 

[ppress79]

Re: Fuel pump shut off

The oil pressure switch turns off the pump if no oil pressure as a fail safe. If the switch is bad, the pump won't prime and you will have to crank as long as a minute to start (as the pump will only pump after it sees oil pressure while cranking and you have to build fuel pressure since it won't prime).
This happened to me awhile back and it was hard to diagnose. I went down the same path as you with relay and even fuel pump before I replaced the switch which fixed the problem and it hasn't returned for me.

Hope this helps,
Phil

 

[canadian]

Re: Fuel pump shut off

The oil pressure switch turns off the pump if no oil pressure as a fail safe. If the switch is bad, the pump won't prime and you will have to crank as long as a minute to start (as the pump will only pump after it sees oil pressure while cranking and you have to build fuel pressure since it won't prime).
This happened to me awhile back and it was hard to diagnose. I went down the same path as you with relay and even fuel pump before I replaced the switch which fixed the problem and it hasn't returned for me.

Hope this helps,
Phil

Nobody has oil pressure when you turn the key to the accessory position which should trigger a short prime of the fuel pump. He states that he doesn't even get that, which I would think rules out the oil pressure switch.

 

[ppress79]

Re: Fuel pump shut off

He doesn't get the prime because the switch is bad. Everything associated with his issue is switch related. The troubleshooting procedure is in the service manual.

Phil

 

[Damian]

Re: Fuel pump shut off

I just checked the trigger wire for voltage when I turn the key on and nothing. I'm not even getting the 12 volt constant right now, but I haven't checked the fuse yet since my 4 month old woke up. I'll check that tomorrow. I'll also go ahead and pick up a new oil pressure switch and put that in, not looking forward to that. Thanks for your help so far, hopefully that's the problem!

 

[Damian]

Re: Fuel pump shut off

I checked all of my fuses, and they are all good. One thing I did notice is that my dome lights don't come on with either door. No idea which fuse that is to be honest. This just gets better and better every day. Also, she won't start up at all now.

 

[canadian]

Re: Fuel pump shut off

He doesn't get the prime because the switch is bad. Everything associated with his issue is switch related. The troubleshooting procedure is in the service manual.

Phil

I figured it would bypass the oil pressure switch if the truck hasn't started (ie: the prime was on a different circuit), but you can't argue with the service manual.

 

[DaveP]

Re: Fuel pump shut off

The oil pressure switch turns off the pump if no oil pressure as a fail safe. If the switch is bad,

Here we go again. NO IT DOES NOT !!!!!


The oil pressure switch has nothing to do with the 2-second "prime" upon key-on.

The oil pressure switch can NOT shut off the pump if the ECM has commanded the RELAY ON at the same time. Which, if the engine is running, the relay will be energized. Oil pressure or not.

Warren: Edit your post. Turning the key to "ACCY" does NOT turn on the fuel pump. You have to turn the key to "IGN".

 

[Damian]

Re: Fuel pump shut off

Pull on the fuse links at the rear of the alternator to check for internal breaks. The dome lights are on the same fuse link as ECM fuse that powers the fuel pump. Also check 4-way flashers and brake lights. Same fuse link.

Are you talking about the 2 cylinder shaped things that are on 2 wires coming off the alternator? I can't see inside them to tell if they are okay or not. I know the other fused wire coming off is for the water pump, which I'm not using, so there is no fuse there.

Okay, I forgot the check the brake lights when I went out there the first time, so I went back out and they work. Okay, checked the constant at the relay and I have my 12 volts back. Okay, opened the door and the dome lights work again. Okay, let's hook the relay back up and see if it starts. Fires right up, less than a second if guess. The only thing I messed with is the wires behind the alt and they all look fine.

 

[Damian]

Re: Fuel pump shut off

They didn't stretch but one pulled out of the ring terminal on the alternator. It's pretty corroded, so I'll fix that here pretty soon.

 

[Damian]

Re: Fuel pump shut off

At least the things I changed did make the engine run better. I just wonder if this is why I've been going through knock sensors left and right?

 

[Damian]

Re: Fuel pump shut off

It runs. I drove it to school without a tow truck being involved. I did notice it didn't want to go above 3 psi, but I was slowly getting into it and didn't want another major problem come up and let off. It is a bit low on gas, but it might also be the cat is clogged. I wasn't able to really gut it properly due to the fact that the muffler shop didn't add an extra flange like I wanted.